The broad objectives of this study will be to characterize the behavior and state of assembly of microtubules in the living cell, to elucidate the mechanism by which microtubules move granules during secretion, and to identify and define microtubular abnormalities leading to secretory dysfunction. Colchicine will be used as a probe to study microtubule regulation in vivo and to detect disorders of microtubule function as well as to study the interaction between secretory granules and microtubules in vitro. Dynein, the putative microtubule ATPase, will be isolated and its enzymic behavior characterized. The role of dynein in granule movement during secretion will be assessed.